1. Field of the Invention
The present invention relates to an imaging unit having an imaging optical system and an image sensor that captures light emanating from a photographic object which is passed through the imaging optical system. The imaging optical system and the image sensor are accommodated in a housing of the imaging unit.
2. Description of the Related Art
In recent years, mobile electronic devices which are designed mainly for taking still/moving photographic images, such as digital cameras (still-video cameras) and digital camcorders (motion-video cameras), and other mobile electronic devices which are designed to have the capability of taking such photographic images as a subsidiary function, such as mobile phones equipped with a camera and personal digital assistants (PDAs) equipped with a camera, have become widespread. In these types of mobile electronic devices, it is common to provide the mobile electronic device therein with an imaging unit which is structured such that an image sensor and a photographing optical system for leading light emanating from a photographic object (object to be photographed) to the image sensor are accommodated in a hollow housing of the imaging unit. Additionally, in recent years, the downsizing (slimming down) of the mobile electronic devices has further progressed, so that the demand to also slim down the imaging unit has become stronger.
Japanese Unexamined Patent Publications Nos. 2008-242446 and 2006-154705 disclose examples of conventional imaging units. Each of these imaging units is provided with a box-shaped housing, and further provided in this housing with an imaging optical system (an incident-side prism, an exit-side prism and lens groups between the incident-side prism and the exit-side prism) and an image sensor, the imaging surface of which faces the exit surface of the exit-side prism in the direction of the thickness of the housing. The traveling direction of light which emanates from a photographic object to be incident on the incident-side prism (which serves as an incident portion of the imaging optical system) changes (i.e., is reflected) at an angle of 90 degrees by the incident-side prism, and thereafter passes through the aforementioned lens groups to be incident on the exit-side prism. Thereupon, the traveling direction of the light incident on the exit-side prism again changes (i.e., is reflected) at an angle of 90 degrees by the exit-side prism so that the light reflected by the exit-side prism exits therefrom through the exit surface of the exit-side prism and is eventually received (captured) by the imaging surface (photosensitive surface) of the image sensor.
Since the imaging units disclosed in the aforementioned two Japanese unexamined patent publications are configured such that the imaging optical system is a bending optical system using prisms, the thickness of the entire imaging unit can be reduced in each imaging unit.
In order for the image sensor of the imaging unit to exhibit a desired imaging capability, the image sensor and the exit-side prism need to be positioned so that the distance (in the direction of the thickness of the housing) between the imaging surface of the image sensor and the exit surface of the exit-side prism corresponds precisely with a designed value (distance).
Although neither of the aforementioned two Japanese unexamined patent publications discloses a positioning device (fixing device) for positioning the imaging surface of the image sensor and the exit surface of the exit-side prism, each of the imaging units disclosed in these two patent publications can make the most of desired imaging capabilities thereof if the exit-side prism and the image sensor are fixed to each other by an adhesive with the distance therebetween being adjusted (a similar technique is disclosed in Japanese Unexamined Patent Publication No. 2010-141865).
However, using an adhesive to fix the exit-side prism and the image sensor to each other makes the installing/assembling of the image sensor and the exit-side prism difficult.
Additionally, if the exit-side prism and the image sensor are fixed to each other by an adhesive with the distance therebetween deviating from a design value or with dust or the like getting therebetween, the exit-side prism and the image sensor need to be bonded again after being separated from each other. However, since it is difficult to separate the exit-side prism and the image sensor from each other after fixing using an adhesive, it is difficult to reuse the exit-side prism and the image sensor.